Adherence to host cells by Candida sp, is essential to the establishment of an infection. This statement is based upon two observations: (1) Species of Candida which adhere to mammalian cells in vitro most often cause candidiasis while those species which do not adhere rarely cause infection; (2) spontaneously derived mutants of C. albicans have been isolated which are non-adhering (or reduced) in vitro and are also avirulent in at 2 least animal models. Therefore, it seems fairly clear that ligand(s) of C. albicans confer virulence to the organism. In this regard, our long-term objective is to identify this ligand(s). In doing so, the host-fungus recognition system will be characterized in part, and, equally important, functional properties of specific cell wall components can be identified. Based upon the observations gained during the previous proposal, purification of the ligand is certainly close-at- hand. Monoclonal antibodies have been developed which identify a 47-kD mannoprotein found only in adhering, virulent wild type C. albicans and not from a derived, non-adhering, avirulent strain (m-10). Fractions of C. albicans wt cell wall which contain this mannoprotein block adherence of C. albicans to human endothelial cells. it would seem therefore that this mannoprotein would have ligand activity. Using a combination of affinity chromatography with monoclonal antibody and high performance ligand chromatography (HPLC), the purification of the Candida ligand will be completed. Once purified, the binding site of the ligand will be determined by using selective enzymatic digestion. The protein will be sequenced and its oligosaccharide component characterized using HPLC. The surface density of the ligand will be determined for various growth forms of C. albicans and as a function of the growth cycle in vitro and expression of ligand examined in infected animals. Functional studies of the ligand are also proposed. Animals will be immunized with the ligand and compared to non-immunized for a protective effect. Both cell mediate immunity and antibody responses to this ligand will be determined. Finally, cell attachment on replicas of SDS-PAGE gels with isolated C. albicans mannoproteins will be used to characterize ligands for a variety of mammalian cell types. in summary, these studies should enhance our understanding of the host yeast recognition system in the pathogenesis of candidiasis.